Summary:
dTDP-4-dehydrorhamnose reductase (RfbD) is involved in the dTDP-rhamnose biosynthesis pathway, which is important for the synthesis of O-specific LPS. dTDP-4-dehydrorhamnose 3,5-epimerase forms a complex with dTDP-4-dehydrorhamnose reductase. The epimerase catalyzes inversion at C-3 and C-5 via corresponding enediols. The reductase then catalyzes the stereospecific reduction of the 4-keto group of epimerase-bound dTDP-4-dehydro-6-deoxy-L-mannose to generate the final product, dTDP-L-rhamnose. [Webb92, Glaser72, Giraud00, Stern99]

The genes encoding the enzymes involved in the biosynthesis of O-specific polysaccharides are clustered in the rfb region. E. coli K-12 does not normally express O-specific LPS due to mutations in the rfb region. However, genes responsible for the dTDP-rhamnose biosynthesis pathway have been identified [Stevenson94].

RfbD has been extensively investigated in Salmonella enterica. The crystal structure has been obtained, a color based enzyme assay has been developed, Mg2+ and NADPH dependence for the reaction has been determined [Giraud99a, Graninger99, Stern99, Blankenfeldt02].